US3262821A - Method for producing cold rolled rimmed steel sheet or strip having non-aging property and superior deep drawability - Google Patents

Description

v fracfz/re HIROSHI YOSHIDA Filed 001;. 8, 1963 fracfure July 26, 1966 METHOD FOR PRODUCING COLD ROLLED RIMMED STEEL SHEET 0R STRIP HAVING NON-AGING PROPERTY AND SUPERIOR DEEP DRAWABILIIY d b/an/r ol'amefer 9 con/co/ 50/7- avg/e ofd/e Draw/1 771roug/1 United States Patent 6 Claims. (Ci. 14s i2.1

The present invention relates to a method for producing a cold rolled rimmed steel sheet or strip having a nonaging property and superior deep drawability.

Heretofore an aluminum stabilized steel sheet has been employed as a cold rolled steel sheet having superior deep drawability and non-aging property. However, the aluminum stabilized steel sheet is lower in yield than the normal rimmed steel one, which results in a higher cost.

In view of the above, I contemplate the provision of a method for producing a cold rolled rimmed steel sheet having superior deep drawing quality as well as non-aging property by the process comprising the steps of providing a relatively inexpensive rimmed steel as a starting material, adding very small amounts of elements thereto, and subjecting the thus produced steel to heat treatment after the cold rolling procedure, whereby an unexpected combined effect of said additives and heat treatment is fully developed.

I have been conducting an extensive research on the beneficial effect of small amounts of additives combined with the heat .treatment in connection with the deep drawing quality and non-aging property of the cold rolled rimmed steel sheet, some results of which have been applied for patents.

This invention is characterized by the method comprising the steps of providing a molten steel containing 0.020 0.150% carbon, 0.150.60% manganese and less than 0.010% phosphorus, adding to said molten steel phosphorus and at least one element selected from the group consisting of antimony, bismuth, niobium and lead so as to produce a rimmed steel containing phosphorus in an amount of 0.0100.040% by weight and at least one element selected from the said group in an amount of 0.0030.050% by weight, making a cold rolled rimmed steel sheet or strip through the known hot and cold rolling procedures, and subjecting said cold rolled steel sheet or strip to a decanburizing and denitriding annealing in an atmosphere effectively promoting the decrease of its carbon content less than 0.020%, preferably less than 0.010%, and of its nitrogen content less than 0.0025 preferably less than 0.0010%.

The cold rolled rimmed steel sheet produced by the above mentioned process has a non-aging property and superior deep drawability represented by an excellent conical cup value determined by the conical cup test specified by the Japanese Industrial Standard Z-2249.

The steel sheet of my invention has a crystallographic orientation favorable for the deep drawing working operation together with a non-aging property in which age hardening will not take place during storage for an extended period of time. The crystallographic arrangement is of the socalled cube-on-corner oriented grain one in which the (111) plane is paralleled to the sheet plane. Many metallurgist-s report that the cube-on-corner orienta- 3,262,821 Patented July 26, 1966 tion is advantageous for the deep drawing steel sheet, but a complete theory thereon has not been established yet. It is believed, however, that it is caused by the directionality of slip of crystal grains under deformation.

A rimmed steel suitable for carrying out my invention is made by the process comprising the steps of providing a molten steel containing 0.02-0.15% carbon, 0.15O.60% manganese, and less than 0.010% phosphorus in a steel making step by means of an open hearth or electric furnace, or a converter, and adding phosphorus and one or more of the elements selected from the group consisting of antimony, bismuth, niobium and lead to produce a rimmed steel containing 0.010-0.040% phosphorus and 0.003-0.050% antimony (bismuth, niobium or lead).

As disclosed in the prior patent applications referred above, phosphorus is effective for improving non-aging and deep drawing qualities. However, when the phosphorus content exceeds a predetermined amount, it will cause the steel sheet to be hardened so that it will give an ill effect to ductility as Well as impact value after working. Therefore 0.040% is preferred to be the upper limit of phosphorus. It should be noted, however, that the phosphorus content derived from a starting material does no benefit for non-aging and deep drawing qualities of the steel sheet product. It is required that phosphorus should be removed from the molten steel as completely as possible in the course of steel making process, and thereafter, a fresh quantity of phosphorus should be added to the steel, which is one of the features of the invention. The reason for this has not been clear, but, based on the experiments, it is necessary that the phosphorus content of the molten steel should be thoroughly removed at least less than 0.010%.

It has been found that an addition of one or more of the elements selected from the group consisting of antimony, bismuth, niobium and lead is not so effective for non-aging quality as that of phosphorus, but the addition of a very small amount thereof is effective for developing a preferred crystallographic orientation suitable for deep drawing in the cold rolled steel sheet of this invention. The amount to be added is so small compared to that of phosphorus that it has been discovered that it is preferred in the range of 0.003'0.050%.

A steel sheet of the final gauge of this invention is produced by subjecting the rimmed steel of the above composition to the known hot and cold rolling procedures. Then, a cold rolled steel sheet of the final gauge thus produced is subjected to a decarburizing and denitriding annealing in a decarburizing and denitriding atmosphere to produce a steel containing less than 0.020%, preferably less than 0.010% carbon and less than 0.0025%, preferably less than 0.0010% nitrogen. The decarburizing and dinitriding atmosphere may be of known one containing, for example, moist H added with about 10% steam or mixture of moist H and N The annealing temperature is preferred between 500 and 750 C. The type of the annealing furnace is not limited. Either batch or continuous type may be used. An open coil type annealing furnace is the most suitable for obtaining a uniform quality of product, and also from a point of view of a Working hour.

Thus, carbon and nitrogen, both of which are deleterious to non-aging and deep drawing properties of steel sheet, are removed while, on the other hand, the crystallographic orientation advantageous for deep drawing is developed.

listed E]. (percent) Chemical Composition (percent) Mechanical properties O.C.V. (mm.)

EXAMPLE 2 Trace Trace Chemical Analysis, Percent Chemical Analysis, Percent Annealing deep drawing and non-aging propert TABLE 1 de-C, de-

de-C, dc-N annealin ing superior the annealed strip coil is subjected to a known skin pass rolling to obtain a cold rolled rimmed steel sheet havin Specimen No. 6 of Table 1.

This steel sheet corresponds to Specimen No. 16 of A steel making process similar to Example 1 is car- Then, ferro-phosphorus (20% phosphorus), metallic This ingot is subjected to the same process as de- Table 1 shows the chemical compositions and various Table 1.

position lead, and term-manganese are added to the above molten steel to obtain a rimmed steel ingot of the following composition:

having superior deep drawing and non-aging properties listed in Specimen No. 16 of Table 1.

mechanical properties of various kinds of known steel lOIl wi metallic Finally, 40 sheet and also of the steel sheet of this invention.

Steel Chemical Compositions, (Percent) do Aluminum stabilized steel Ordinary anncaling Rimmed steel added with P and Sb- Rimmed steel added with P and Bi".

Rimmed steel added with P and N b.

Thereafter, this steel scribed in Example 1 to produce a cold rolled steel sheet hiefly of scrap and p iron is refined by the known basic open hearth furnace process in the steel making process with a special attenphosphorus),

Specimen No.

Speci- 1 Normal rimmed stcel Ordinary annealing.

5, do do 7 .e. do.

ing 0 EXAMPLE 1 This example corresponds to Specimen No. 6 of the 5 sheet listed in Table 1.

Chemical Analysis, Percent Trace -manganese are added to the molten into a mold to obtain a rimmed steel t of the following composition Chemical Analysis, Percent Trace mg composition:

-phosphorus (20% This invention is now described in connect the following examples.

A steel material consist tion to dephosphorization to obtain a steel of the follow- 10 ried out to obtain a molten steel of the following com- Then, ferro antimony and ferro steel, and poured ingo Then, the steel ingot is subjected to the known hot and cold rolling procedures to obtain a cold rolled steel strip coil of 0.8 mm. in thickness. strip coil is subjected to a decarburizing and denitriding anneal in an atmosphere consisting of H N mixed gases, 75% H and 25% N added with about 10% H O in an open coil type annealing furnace at the temperature of 700 C. for a period of hours.

See footnote at end of table.

Mechanical Properties Intensity of Specimen (111) plane No. '1.S. Y.P. YE. Y.E. after Increase in diffraction (kg/mm?) (kg/mm?) (percent) 6 months Y.E. during peak (percent) 6 months 1 Drawn through.

Referring to Table 1, Specimen No. 1 refers to a noris obtained. In general, as the R value depends on the mal rimmed steel sheet of the commercial grade, No. 2 direction from which the test specimen is taken, the measto a normal rimmed steel sheet subjected to a decarurement along the three directions, rolling direction (R burizing and denitriding annealing, and No. 3 to an alumi- 45 degrees to the rolling direction (R and 90 degrees num stabilized steel sheet widely employed for deep to the rolling direction (R is made, and the mean 'i n gp ll l l refer to The value E is obtained from the following formula: co d ro e rimmed stee s eet produced in accordance with this invention. i +2(R45) In reference to the mechanical properties, plastic strain ratio (R), conical cup value (C.C.V.), elongation (EL), The Japanese Industflal Standard, relatlng Erichsen cup value (EL), tensile strength (T.S.), yield point (Y.P.), yield point elongation (Y.E.), Y.E. after six months, increase in Y.E. during six months, and the intensity of (111) plane diffraction peak by the X-ray inverse pole figure method are shown.

The plastic strain ratio, R, is a value showing the deep drawing property and the preferred orientation suitable for the deep drawability of the steel sheet, and can be obtained from the following formula:

log W o/W R log t /t where The greater the R value the less thinning in the thickness direction in the plastic deformation, and the more the deformation in the width direction.

It follows that the steel sheet material having a large R value is excellent in the deep drawing property, since the fracture in the deep drawing process is caused by the necking due to the decrease of sheet thickness. As a matter of fact, in obtaining the R value, it is difficult to conduct an accurate determination of the thinning in the thickness direction. So we measured the elongation of gauge length of the tensile test specimen by means of the electronic strain meter and the mean width of the specimen. The R value is obtained from the following formula, provided that the volume of the deformed test specimen being constant:

l -W -t =l-w-r where l gauge length before tension gauge length after tension log W /W log l-w/l -w By the above measurement, the test errors are very small. For this test specimen, a tensile test specimen (gauge length 50 mm.) of I IS (Japanese Industrial Standard) No. 5 is employed, and the R value in 15% extension to the method of conical cup test, has been recently published. In this conical cup test, it is possible to draw a steel sheet without forming wrinkles and without applying nay blankholder pressure provided the correct blank diameter is selected with respect only to sheet thickness. The effect of bending and unbending, which is an important factor in a cylindrical cup-forming test, is also less important in the conical cup test. A hemispherically ended punch with a profile radius of approximately 5 to 10 times the thickness of the test blank is used. The rating of drawability is obtained from the average diameter of the rim of the conical cup when fracture occurs. Since the blank diameter is fixed only by the sheet thickness, the test is simple and quick.

The principle of the test is illustrated in FIG. 1. A circular blank is rested horizontally in the conical die, and drawn with the appropriate punch until the bottom of the cup fractures. The dimensional specifications are given in Table 2.

The die hole diameters specified are such that no ironing of the cup occurs as it enters the die hole. Blanks should be cleaned and then lubricated and the speed of drawing is virtually immaterial.

The conical cup-forming test of the Japanese Industrial Standard, Z2249, is performed in an arrangement of tools for a conical cup test shown in the accompanying drawing, in which:

FIG. 1 shows a sectional view of the arrangement of tools for the conical cup test.

FIG. 2 shows a perspective view of a shape of fractured cup as the result of test.

FIG. 3 shows a perspective view of another shape of fractured cup.

FIG. 4 shows a perspective view of a shape of a completely drawn cup with no fracture.

More particularly, the conical cup value (C.C.V.) is represented by the numerical value, mm., of the average diameter of the rim of the conical cup when fracture occurs as shown in FIGS. 2-3. The conical cup value shown in FIG. 3, which is less than that of FIG. 2, is obtained from the steel sheet having a better deep drawability than that of the one shown in FIG. 2. The shape of the completely drawn cup with no fracture shown in FIG. 4 is attained by the steel sheet of a very high deep drawability, and in this case, no value of conical cup 7 test is obtained, but represented as drawn through in Table 1.

In order to obtain the conical cup value (C.C.V.) of a steel sheet of a particular thickness, the particular tools specified by I IS Z-2249 as shown in Table 2 should be employed. C.C.V. of various steel sheet listed in Table 1 are the measurements conducted on the sheet of the thickness, 0.8 mm. by means of the die type 17 of Table 2. In Table 3, the minimum standard value for showing the drawability of each sheet of a particular thickness produced by the process of this invention is listed.

C.C.V. of the sheet of Sheet Thickness, mm. Die Type, 518 this invention.

1 Or less.

A series of tensile test, such as, elongation, tensile strength, yield point, and yield point elongation, are conducted on Specimen No. 5 having the gauge length, 50 mm., specified by 115. An Erichsen cup test is carried out by means of the ram head with the radius of As clearly shown in the E value and the X-ray intensity of (111) plane diffraction peak of Table 1, the crystallographic orientation of the rimmed steel sheet of this invention, namely, Specimen Nos. 4 to 16, is different from that of the normal rimmed steel sheet.

Thus, the X-ray intensity of (111) plane'dilfraction peak of the normal rimmed steel sheet is small while that of the steel sheet produced from the normal rimmed steel which has been subjected to the decarburizing and denitriding annealing is also relatively small.

Compared to the above, the accumulation of the main crystallographic orientation (111) of the steel sheet of this invention is stronger.

The intensity of (111) plane diffraction peak of the aluminum stabilized steel is stronger than that of the normal rimmed steel, but weaker than that of the steel sheet of this invention. The above-mentioned re'lation ship is made more distinct in the E value of Table 1. Thus, the E value of the normal rimmed steel is the least of all, that of the decarburized and denitrided rimmed steel larger, and that of the aluminum stabilized steel the largest. The E value of the steel sheet of this invention is also equal to or larger than that of the aluminum stabilized steel.

In case (111) plane is parallel with the rolling surface, the fact that the E value is made large can be explained theoretically as follows: when the slip direction is only (111) direction while deformation, and when (111) plane is parallel with the rolling surface, it is explained by mathematical analysis that the strain in the sheet plane direction becomes larger than that in the thickness direction.

In Table 1, the conical cup value of the rimmed steel sheet of this invention is good, and particularly, the test Specimens of No. 6, 7, 10, 11 and 16 are drawn through without fracture, respectively.

As described hereinabove, a favorable effect of phosphorus and antimony, bismuth, niobium or lead on the deep drawing quality of the steel sheet is apparent. However, in the practical press forming process, the formation of miscellaneous complicated shapes is required so much that not only the high degree deep drawability but also the high stretch formability should be given to the steel sheet. In reference to the characteristic value for showing stretch formability, both elongation, El., and the Erichsen cup value, Er., are universally adopted.

As clearly illustrated in Table 1, the steel sheet of this invention has a good conical cup value and Ti value as well as good El. and Er. values.

The test value for showing an aging property of steel sheet is shown by the change of yield point elongation of a test sheet left for a period of six months. As clearly illustrated in Table 1, the increase in yield point elongation of the steel sheet of this invention is hardly observed or so small that the non-aging quality thereof is as excellent as that of the aluminum stabilized steel sheet well known for its non-aging.

Various changes and modifications of this invention can be made and, to the extent that such variations incorporate the spirit of this invention, they are intended to be included within the scope of the appended claims.

I claim:

1. A method for producing a cold rolled rimmed steel sheet or strip having non-aging property and superior deep drawability comprising the steps of: (1) providing a molten steel containing 0.0200.150% carbon, 0.15- 0.60% manganese, less than 0.010% phosphorus and the remainder being essentially iron, (2) adding to said molten steel phosphorus and at least one element selected from the group consisting of antimony, bismuth, niobium and lead so as to produce a rimmed steel containing phosphorus in an amount of 0.010-0.040% and at least one element selected from the said group in an amount of 0.0030.050%, (3) forming a rimmed steel sheet or strip by hot and cold rolling, and (4) subjecting said cold rolled steel sheet or strip to a decarburizing and denitriding annealing to decrease the carbon content to less than 0.020% and the nitrogen content to less than 0.0025

2. The method according to claim 1 wherein the decarburizing decreases the carbon content to less than 0.010%.

3. The method according to claim 1 wherein the denitriding decreases the nitrogen content to less than 0.0010%.

4. A cold rolled rimmed steel sheet or strip having nonaging property and superior deep drawability consisting essentially of less than 0.020% carbon, 0.150.60% manganese, 0.010-0.040% phosphorus, 0.003-0.050% of at least one element selected from the group consisting of antimony, bismuth, niobium and lead, less than 0.0025% nitrogen, and the remainder being essentially iron.

5. The steel sheet or strip in accordance with claim 4 wherein the carbon content is less than 0.010%.

6. The steel sheet or strip in accordance with claim 4 wherein the nitrogen content is less than 0.0010%.

References Cited by the Examiner UNITED STATES PATENTS 3,188,246 6/1965 Olt et a1 14816 3,193,417 7/1965 Kopchak 14831 3,215,567 11/1965 Yoshida 148-31 DAVID L. RECK, Primary Examiner.

H. F. SAITO, Assistant Examiner.

Claims (1)

1. A METHOD FOR PRODUCING A COAL ROLED RIMMED STEEL SHEET OR STRIP HAVING NON-AGING PROPERTY AND SUPERIOR DEEP DRAWABILITY COMPRISING THE STEPS OF: (1) PRIVIDING A MOLTEN STEEL CONTAINING 0.020-0.150% CARBON, 0.150.60% MANGANESE, LESS THAN 0.010% PHOSPHORUS AND THE REMAINDER BEING ESSENTIALLY IRON, (2) ADDING TO SAID MOLTEN STEEL PHOSPHORUS AND AT LEAST ONE ELEMENT SELECTED FROM THE GROUP CONSISTING OF ANTIMONY, BISMUTH, NIOBIUM AND LEAD SO AS TO PRODUCE A RIMMED STEEL CONTAINING PHOSPHORUS IN AN AMOUNT OF 0.010-0.040% AND AT LEAST ONE ELEMENT SELECTED FROM THE SAID GROUP IN AN AMOUNT OF 0.003-0.050%, (3) FORMING A RIMMED STEEL SHEET OR STRIP BY HOT AND COLD ROLLING, AND (4) SUBJECTING SAID COLD ROLLED STEEL SHEET OR STRIP TO A DECARBURIZING AN DENITRIDING ANNEALING TO DECREASE THE CARBON CONTENT TO LESS THAN 0.020% AND THE NITROGEN CONTENT TO LESS THAN 0.0025%.

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